Frequently in downhole equipment there are narrow annular spaces that can be exposed to well fluids that have a fair amount of debris. The debris can get into small spaces and stick equipment which can have the negative result of keeping components from moving relatively when needed for either setting tools or releasing tools.
Various designs for debris barriers have been proposed. Some involve components that fold on each other to span an annular space and close it off. These designs can act similar to seals and this can create other issues such as liquid locking of relatively moving parts if fluid in volumes that are made smaller has no escape route or conversely with volumes that are made larger there being no way for fluid to enter hence the liquid locking problem. Some folding debris barrier design are U.S. Pat. No. 6,896,049 and U.S. Pat. No. 7,604,048. One solution to the liquid locking problem is to provide a bypass with a rupture disc as shown in U.S. Pat. No. 8,881,802. Other designs simply fill an irregular space with foam to keep debris out of dead end spaces that are not annularly shaped. U.S. Pat. No. 8,464,787 shows odd space filling and annular members that are stated to stop debris while allowing pressure to dissipate across the barrier. This design that uses foam is for generally light debris applications as the foam lacks structural integrity when large debris loads land on a barrier made from that material. What can then happen is compaction to the point where the porous member can become impervious thereby bringing up the liquid locking problem described above. Additionally, closed-cell foams and open-cell foams that have lost their permeability may trap compressible liquids or gases, leading to a decrease in volume under pressure. This can prevent the foam from acting as an adequate barrier. Other designs, such as US 2010/0288492, add complexity to the debris barrier design with sensors to detect blocking that can alert surface personnel to stop pumps or to reverse flow direction to clear the barrier. These solutions are not always practical in limited space environment where a simple structure is needed to perform the desired function without taking up a lot of space. Other designs feature a loose fitting ring member to fill an annular space with opposed grooves to trap what solids migrate into the clearance space. This design is effective for some applications but in heavy debris environments the debris can clog the grooves and even put the rings askew to let pass an undesired amount of solids. Such designs are shown in U.S. Pat. No. 8,631,863 and U.S. Pat. No. 8,794,313. Finally there are cup shaped seals with backup rings that can be impervious which leads to the potential of liquid locking depending on the direction of relative movement. Even when alternative materials are used, as suggested by this reference, there can still be problems when there is relative movement that can contort the cup shape or mar one of the opposing surfaces that define an annular gap. U.S. Pat. No. 7,905,280 mentions the use of a metal wire brush material in the context of an actuated seal that has a cup shape in a context where there is no relative movement between the parts.
The present invention provides a simple design for an annular gap between downhole components that may be filled with gel or clean fluid as one avenue of eliminating the incursion of debris. However, the relative movement between a running string and a surrounding liner top having an external hanger/packer can urge the gel or clean fluid to move as volumes decrease so that the barrier needs to be porous and/or flexible enough to let a gel pass while at the same time it needs to keep out the debris and have enough structural rigidity to support the debris if there are large accumulations without experiencing a structural collapse from loading. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.